Developing unusual effects with unique appearance and glamorous colors has never been easier due to the wide variety of special-effect pigments on the market today. Designers can choose from dramatic color shifts to the subtler and increasingly popular metallic colors found on everything from automobiles, appliances and electronic componentry to many general industrial, ink and plastic applications. By far the most utilitarian and popular pigment for special-effect aesthetics has been aluminum. Its popularity has played a major role in color trends throughout the past 60 years, and has been a dominant pigment in the color palette for the last four years. The millennium color, "Silver" not only imparts a feeling of richness, but also technical precision, and its popularity is expected to continue into the foreseeable future.

Aluminum pigments are not new, and in fact have been formulated into coatings, ink and plastic applications for many years. Originally designed as a functional pigment, leafing grades were applied to steel structures providing a barrier protection that was second to none. As aluminum pigment technology grew, it soon became apparent that unique effects could be achieved if the pigment was "deleafed". Allowing the flake to reside within the film matrix, rather than at or near the surface, creating a whole new color space for designers to work with. Polychromatic or ‘metallescent' colors provided exciting new ways to market anything that could be coated. Designers from all parts of the color world quickly acknowledged the aesthetic appeal and began using non-leafing aluminum pigments.

A Challenging Need

The traditional aluminum pigment that everyone is familiar with is a metallic flake suspended in an aliphatic or aromatic solvent, and supplied in paste form. It is usually supplied in a steel drum containing from 50 to 250 lbs, and is readily usable and dispersible in solvent systems. The somewhat non user-friendliness of this paste, coupled with changes in coatings technology in recent years, have provided some driving challenges that the aluminum pigment industry has needed to address. The principle challenges are the demand for a safe, easy-to-use product, that is solvent free and easy to use in waterborne coating systems. While a major shift toward waterborne coatings technology has occurred over the last 20 years, aluminum pigments are still made using an organic solvent. Simply put, aluminum pigments are for the most part, still ball milled in mineral spirits, and provided to the customers in the same paste form. Removal of the mineral spirits is possible, but results in a "messy-to-handle product", and more importantly a product that must be handled properly to ensure safe use. A major shift from solventborne to waterborne coatings occurred over the last 15 to 20 years - how does a pigment produced and supplied in an organic solvent meet the industry needs?

Meeting the Challenge

Silberline has always been proactive in attacking problems based on customer needs. However, the challenge to develop a safe, easy-to-use, water-dispersible product with zero VOCs was not something that could easily be accomplished. Silberline researchers tackled this challenge by attacking three basic needs:

1. The product had to be safe, easy to use and have zero VOCs.

2. The product had to disperse easily in water, and remain stable with little or no gassing, and

3. The product had to aesthetically perform as well as commercially available aluminum pastes.

The first challenge, to supply a product form that was safe and easy to use, with zero VOCs, required the removal of all solvent from the paste. Easy to do, but replacement of the solvent with some type of binder was necessary to eliminate the problems associated with a dry flake. Silberline researchers had earlier developed and patented a pellet technology, commercially referred to as Silvet (Figure 1).

This unique technology was designed to remove all of the solvent from the flake, replace it with a resinous binder, and supply the product in a pellet form. The applications for this product form included a wide range of products designed for solventborne inks and coatings, and the plastics markets. The fundamental benefits of this technology had been realized through commercial success and, therefore, were considered the building blocks or foundation for this new technology. The concepts of safety and ease of use are synonymous with the Silvet technology. The flake, when embedded in the resinous matrix, has a significantly limited chance of becoming airborne, and thus reduces the opportunity for an explosive condition. The resinous matrix, because it binds the flakes together, also provides a degree of cleanliness not found in aluminum pastes. A user can easily handle the pellets without the normal smearing of the flake on every surface it comes in contact with. This offers several very important advantages in both packaging and dispensing the product. No solvent, no evaporation. The pellet is packaged in heat-sealed bags that prolong the shelf life of the product, and offer the user an easy-to-handle, easy-to-store and easy-to-dispose package. Dispensing the product is simple; slit the bag, and pour the pellets out - no dust, no messy paste clinging to dispensing equipment, etc.

The second need, or goal, was to design a resin matrix to carry the flake that would disperse easily in water, be compatible with many ink and coatings systems, and have good gassing-resistant properties. The research screening process involved many variables, but resulted in a binder based on melamine resin chemistry. The resin selected was perfectly suited for pellet processing, producing a pellet-shaped granule with good integrity. Pellet integrity is an important aspect of safety and is necessary to avoid excessive dust generation. Additionally, the resin provided excellent film-forming properties to the finished coating/ink application. The characteristic most sought after in the research process, however, was ease of dispersion in water. In this case, the ease of dispersion exceeded expectations. The final product literally melts into water during the dispersion process (Figure 2).

Part of the "package" to carry the aluminum was the need for an inhibition system that would prevent the aluminum/water reaction that results in the generation of hydrogen gas. Silberline's expertise in this area has been second to none. A number of inhibiting chemistries were available from our repertoires that were carefully considered from a performance standpoint. The final chemistry was specifically tweaked and designed for this product and has resulted in one of the most optimized gassing-resistant systems available on the market today. Gassing studies in a standard latex coating system have demonstrated less than 15 ml of hydrogen generated using a standard gassing test method (Figure 3).

The final piece of the development puzzle was to ensure that the product performed aesthetically as well as the standard paste product, and maintained a minimum shelf stability expected by our customers. Chemical or mechanical damage during processing needed to be minimized to maintain the "effect" that the aluminum flake was designed to achieve. Following the principles of our Silvet technology, and applying techniques designed to enhance performance, the final process exceeded expectations. Not only did we have a process that had little effect on flake appearance, but we also had a product with excellent shelf stability. Internal accelerated testing indicated excellent stability with no loss of properties.

Composition and a New Name

In keeping with tradition, it seemed natural to name this new family of grades based on composition and end use. Aquavet, a waterborne pellet with multifunctional application, seemed to be the right fit. The final composition of this new product was optimized to again meet customer needs, maintaining the aluminum flake loading at 80%, with 11% resin carrier and 9% inhibition package. This composition gives the finished pellet the physical integrity and also provides the customer with optimized loading of the metal flake.

Concept to Prototype and Formulation Development

Aquavet prototype development was further proven in actual formulations to confirm development results and assure commercial acceptance and success. The multi-functional properties of the melamine resin carrier permit use in a variety of coatings and ink applications, and suggested formulations and tips were generated for starting-point customer use. The Aquavet technology has been successfully applied to both leafing and non-leafing grades to further support customer needs.

Summary

Aquavet technology provides the end user with many advantages not found in standard aluminum pastes. Designed specifically for waterborne applications, these pellets will gain rapid acceptance because of their many advantages including:

Non dusting

-explosion hazard reduced
-cleaner plant environment

Dispersion ease

-broad system compatibility
-almost "melts" into water

Dispensing ease

-pours out of the container/easy to meter very easy to handle

Complete utilization

-offers reduced waste; the entire product comes out of the container easier container disposal

For more information, contact Silberline Manufacturing Co., Inc., 800/348.4824, or visit www.silberline.com.

Starting-Point Waterborne Ink Formulation

Aquavet 251 - 136M 18.7
Deionized Water/Glycol Ether (6:1 ratio) 18.0
Latex Ink Vehicle* 39.1
Reduce with Deionized Water 24.2

Starting-Point Waterborne Coating Formulation

Aquavet 251 - 136M 17.6
Deionized Water/Glycol Ether (4:1 ratio) 17.6
Latex Coating Vehicle (Solids)* 56.7
Texanol 6.6
Ammonia 1.0
Anti Foam Agent 0.5

Formulation Comments/Incorporation Suggestions:

* A variety of latex ink and coating vehicles are available on the market. More information on appropriate vehicles and well-defined formulations are available.

Incorporation Suggestions:

Add aluminum to mix tank before adding other components;

Add about 1/3 of the water/glycol ether mixture and allow to soak;

Stir slowly with good shear until creamy dispersion has been achieved;

Slowly add remaining water/glycol ether components and resin while stirring;

Additives/surfactants can be added to cosolvents prior to addition to composition;

Deionized water can be added to composition for viscosity adjustment;

Avoid shocking and agglomeration issues by adding above components in stages;

Maintain pH on alkaline side ~ 8.5;

Maintain simplicity in the formulation to enhance stability.